Visual Impairment and Dementia in the UK Biobank Study
September 23, 2021
Written by Bruce P. Rosenthal OD, FAAO,Chief of Low Vision Services, Lighthouse Guild
Eye care clinicians, especially those specializing in the management of low vision patients, are routinely faced with patients who are not only severely visually impaired but at risk of developing dementia as well. In fact, there appears to be a dual medical crisis looming on the horizon—especially with the numbers of persons diagnosed with visual impairment (VI) and blindness predicted to double by 2050, while the expectations for dementia, which currently affects 46.8 million people worldwide, predicted to triple by 2050.
The objective of this study involving 117,187 participants was to investigate the association of VI, as well as the risk, early prevention, detection, and huge burden of dementia. The literature involving the association of VI and dementia, however, has been limited by small sample sizes and self-reported visual function, and basically has concentrated on late-stage dementia.
The large-scale study with VI severity and incident dementia, investigated persons aged 40 to 69 years. The ophthalmic assessments used for the study were impressive. with logMAR (logarithm of the minimum angle of resolution) visual acuity (VA), autorefraction, intraocular pressure (IOP), keratometry, corneal biomechanics, and spectral-domain optical coherence tomography (OCT) imaging.
VA was measured in 23.3% of the 117,252 participants in the UK Biobank Study. VA was classified as mild (0.3< logMAR ≤0.6; Snellen VA <20/40 to ≤20/80), moderate (0.6< logMAR ≤0.7; Snellen VA 20/80 to ≤20/100), and severe (0.7< logMAR; Snellen ≤20/100).
The dementia cases combined participants’ medical history, linkage to hospital admission, and the national death registers. Confounding variables known to be associated with dementia, including age, sex, and ethnicity, were included in the study. Other factors taken into consideration included family history of dementia, smoking status, and comorbidities, such as depression, diabetes, hypertension, and hyperlipidemia.
Although the initial group was not diagnosed with dementia at the baseline assessment, 3.43% of the 4018 participants (out of 117,187) had VI, and those with the greatest risk for dementia (0.37%) were those with severe VI.
The authors noted that VI might be one of the first indicators of dementia. This may be a result being more likely to be isolated socially, predisposed to depression, diminished visual information, and even decreased physical activity. One of the other important considerations noted is that beta-amyloid deposits and genetic risk factors for dementia are similar to those found in patients with age-related macular degeneration.
The authors suggest that VA testing may be a very valuable tool in identifying individuals at risk for cognitive decline and dementia. The eye care community and especially low vision clinicians who manage patients with severe VI appear to be the conduit in helping to screen patients who are at high risk for dementia. However, low vision clinicians, who are involved in vision rehabilitation, routinely evaluate VA at different test distances (eg, ETDRS 4M, 2M, 1M), resulting in the ability to measure VA well beyond 0.7<logMAR (Snellen ≤20/100) and up to 1.6 logMAR (20/800).
In future studies, it would be beneficial to evaluate the risk of dementia, comparing the results of the graded sample of incident dementia in the present study to those persons with profound vision loss as noted above. It would also be very valuable to evaluate, as the authors note, other components of visual impairment, including contrast sensitivity (CSF). CSF has been a valuable vision rehabilitation tool, used by low vision clinicians (since the early 1980s). More importantly, CSF may be another valuable predictor in the risk of developing dementia.
The testing of VA and risk of dementia is an extensive groundbreaking study that brings to the forefront the value of VA testing. Nevertheless, the UK Biobank Study also notes the need for evaluating other components of visual function as well as the importance of vision rehabilitation in order to help those who are socially isolated, depressed, and unable.